The proposed project builds on an existing trial of micronutrient supplementation on children's growth, immune functioning, and morbidity, administered from birth through 9 months among full-term infants born small-for-gestational age in a low-income community in India. The trial had four cells: riboflavin with and without zinc, and other micronutrients [riboflavin, calcium, phosphorus, folate, and iron] with and without zinc. In April 1999 the children will range in age from 14 to 32 months, providing a unique opportunity to examine the protective effects of early micronutrient supplementation on children's behavior and development during the second and third years of life when the children are consuming community diets. We will use a cross-lag panel design to follow 600 children who participated in the micronutrient supplementation trial and a comparison group of 225 children, born at term with birth weight appropriate for gestational age. Children will be studied in clinical and home settings at 18, 24, 30, and 36 months of age to determine if differences in behavior and development are related to: (i) the micronutrient supplementation they received during infancy and (2) the timing and duration of their micronutrient deficiency during toddlerhood. The project tests the theory of functional isolation which hypothesizes that the lethargy and social isolation that often accompany nutritional deficiency interfere with reciprocal, stimulating interactions with caregivers, thereby leading to developmental and behavioral delays. The design and analysis are based on an ecological model in which behavior and development are influenced by birth weight, supplementation history, growth, temperament, parent-children interaction, and family environment contribute to children's behavior and development. Analysis will be conducted by longitudinal strategies, including multiple regression and hierarchial linear modeling. The results have important public health implications regarding the timing of micronutrient supplementation and the relationship between micronutrient deficiency and children's behavior and development.